Add shelljs based release script

package.json

@@ -46,6 +46,7 @@
     "concat-stream": "^1.5.0",
     "geopkg": "^4.0.3",
     "istanbul": "^0.4.1",
+    "shelljs": "^0.5.3",
     "standard": "^5.4.1",
     "tape": "^4.0.1"
   },

release.js

@@ -0,0 +1,36 @@
+var shell = require('shelljs');
+
+if (exec('git status --porcelain').output != '') {
+  console.error('Git working directory not clean. Please commit all chances to release a new package to npm.')
+  process.exit(2);
+}
+
+var versionIncrement = process.argv[process.argv.length -1]
+var versionIncrements = ['major', 'minor', 'patch']
+
+if (versionIncrements.indexOf(versionIncrement) < 0) {
+  console.error('Usage: node release.js major|minor|patch')
+  process.exit(1)
+}
+
+exec('npm test')
+
+exec('npm geopkg')
+exec('git commit -m "Geotag package for release" package.json')
+
+exec('npm version ' + versionIncrement)
+
+exec('git push')
+exec('git push --tags')
+exec('npm publish')
+
+function exec (cmd) {
+  var ret = shell.exec(cmd, { silent : true })
+
+  if (ret.code != 0) {
+    console.error(ret.output)
+    process.exit(1)
+  }
+
+  return ret
+}